The invention relates to a method for measuring electrical resistance of thin metallic layers or films manufactured under the influence of a plasma. A direct current or ohmic resistance measurement according to the principle of the two point-or four point-measuring method is provided. The invention also relates to applications of the measuring method.
As is known from an article of Hieber and Mayer from Thin Solid Films, 90 (1982), pages 43 to 50, incorporated herein by reference, the measurement of the electrical resistance of metallic films during the film manufacture makes it possible to determine already during the film manufacture, changes of structure, alloy composition, and/or microstructure.
In fabrication, for example of printed circuits in semiconductor technology, metallic layers are most frequently manufactured in cathode sputtering systems (sputter systems) with vacuum load locks. During the coating, the semiconductor crystal substrates to be coated are constantly moved or rotated back and forth under one or more sputter targets. An apparatus which makes it possible to measure the electrical resistance of films during the manufacture in cathode sputtering systems (sputter systems) with a vacuum load lock and a moved (rotatable) substrate pallet, is described in the Siemens Research and Development Reports, Vol. 11 (1982), No. 6, on pages 322 to 326 in an article by N. M. Mayer and the European Patent Application No. 0 067 432, both incorporated herein by reference. The resistance measuring device with a measuring data transmission system is here mounted on the side of the substrate pallet not facing the cathode sputtering plasma (sputter plasma). The resistance measurement proceeds with the known four point-measuring method in the case of D.C. current. The measured resistances are transmitted by radio from the coding chamber to a receiver outside the sputter system, and from there are transferred to a computer for data storage and evaluation.
Measurements with this measuring apparatus on tantalum layers during the manufacture with a DC-magnetron can be learned from the already cited Siemens Research and Development Reports, Vol. 11 (1982) No. 6, pages 332-326, incorporated herein by reference.
If the electric film resistance is measured in dependence upon the time, the resistance is then lowered gradually or in steps with each sputtering-on of a new film layer. In this regard, reference is made to FIG. 1, which represents in a diagram the resistance progression in dependence upon time in the case of the layer-wise coating of a substrate with tantalum during RF-diode-sputtering. Plotted as the ordinate is the resistance in ohms. Plotted as the abscissa is the sputter time in sec. However, if the film approaches the sputter target and thus the influence region of the plasma necessary for the cathode sputtering, the measured electric resistance becomes falsified. In FIG. 1, this is visible by the peaks at each stage. The expansion, position, and the energy content of the sputter plasma in the coating chamber is dependent upon the sputter conditions, the sputter method (i.e. sputtering two or more targets simultaneously (co-sputtering) in the modes RF (radio frequency)-sputtering and/or DC (direct current) sputtering with or without magnetron), and the sputter performance. Influencing of the electrical measurements is particularly great in the case of RF sputtering or in the case of sputtering of several targets simultaneously. In these cases, it is at least partially no longer possible to measure the electrical resistance of the film without the influence of the plasma during a pallet rotation since the sputter plasma extends over the entire coating space, whereas the plasma in the case of DC sputtering of a target with low power is disposed only in a proximity of the target.